The Tokyo 2020 Olympic Marathons: Spectator Thermal Comfort and Health in the Face of Extreme Heat

The 2020 Olympic Games marathon will be run through the streets of Tokyo on the mornings of August 2^ndand 9^th, a time of year that is typically hot, sunny, and humid. Few studies have assessed the potential impact of extreme heat along the marathon course to understand multiple factors (e.g., radiation, wind flow) influencing human thermal comfort (TC) as influenced by urban design and forestry.

The current research establishes a baseline of microclimate conditions and scenarios to estimate the projected TC along the marathon course for spectators. Mobile microclimate data (air and surface temperature, solar radiation, humidity, wind speed) were collected over 15 periods in the summer of 2016 and aligned with sky view factors (SVF). Human energy budget modeling was applied to provide spatially-explicit heat budget and thermal comfort information across various days and scenarios.

Conditions are expected to be the most uncomfortable along the open, sun-exposed locations, with ~50% of the area along the second half of the course resulting in ‘Hot’ (budget>200 Wm^-2)or ‘Very Hot’ (budget>295 Wm^-2) conditions that are linked to heat stress largely caused by minimal shade. The heat strain index (HSI) frequently rises above 80%, with high vapor pressure and low wind flow exacerbating discomfort. Buildings and trees providing a low SVF over roads and sidewalks protect spectators from the morning radiant heat, but such locations should be balanced with wind flow to optimize comfort.

The modeling and spatial information can aid in preparing for and mitigating heat stress during the Olympics, working in conjunction with local organizers and government. This 'research through design' strategy can aid in preparing for and mitigating heat stress along the marathon route during the Olympics, and the knowledge gained can be extended to other areas of Tokyo to reduce the urban heat island and further provide targeted guidance for effective green infrastructure.